1. The Field of the Invention
This invention relates to movable support frameworks. More specifically, this invention relates to foldable scaffolds.
2. Present State of the Art
Masonry and carpentry are two of many jobs that require the use of scaffolds. Scaffolds assist workers by allowing them to work in elevated positions. However, scaffolds have several challenges. Scaffolds must be transported to and from the workplace. Scaffolds must be assembled and disassembled. Additionally, scaffolds must be stored when they are not in use. All of these activities require time, and these conditions are compounded when the work area is small and confined or when a scaffold is moved from location to location through narrow openings. Any time a scaffold is moved, whether it be from one workplace to another or simply to another location at the same workplace, an additional assembly and reassembly of the scaffold is required.
With a conventional scaffold, the scaffold must be disassembled and then reassembled as the work location requires. The economic impact on the employer is profound, as the workers must be paid for their time. An employer would prefer to pay workers for work done on an employer's contractual obligations, rather than for time spent transporting, assembling, disassembling and storing scaffolds. Further, a project is delayed by the time workers spend transporting, assembling, disassembling and storing scaffolds. One significant advantage of conventional scaffolds is that they are rigid and enable workers to be securely supported.
The prior art discloses foldable scaffolds that have attempted to solve the time consuming problems presented by conventional scaffolds while maintaining sufficient rigidity. U.S. Pat. No. 5,099,953, issued to Stegath, discloses a foldable scaffold that has two end ladders and one horizontal truss. The truss has as many as four locations where the scaffold must pivot in order to fold. One pivot exists at each ladder post and the truss has a gate portion with two pivots. The scaffold folds like an accordion. The simplest configuration of this scaffold only has three sides. In an effort to maintain rigidity, the supporting planks are securely fastened to the rungs of an end ladder. A workman typically attaches the planks to the uppermost rung. In that case, one entire side of the scaffold has horizontal stability only at the top of the end ladder, while the lower portion of the scaffold no longer has rigidity because it has no stabilization. Another aspect of this scaffold is that it is one permanently connected piece. The truss is permanently connected to an end ladder. The scaffold is essentially one integral component and this aspect makes the scaffold difficult to store compactly and efficiently for two reasons. First, the folded scaffold is large and the truss and end ladders are free to rotate. Second, the scaffold, in its folded position, has an awkward shape.
U.S. Pat. No. 5,069,309, issues to Swiderski et al., discloses a rolling tower scaffold that has two end ladders and a horizontally extending support platform which is adjustably mounted between the end ladders. This platform is supported by a frame that has carriage rails that slidably engage the end ladders. The engagement of the carriage rails to the end ladders is such that it only allows for motion of the carriage rails along the vertical rails of the end ladders, but no rotation of the frame with respect to the end ladders is allowed. In this configuration, the tower scaffold must be disassembled when it has to be moved through an opening that is narrower than the end ladders. In other words, the fully assembled configuration of the tower scaffold disclosed in this patent cannot be distorted into shapes other than the fully assembled working configuration. Furthermore, the tower scaffold disclosed in this patent cannot be configured as a stair scaffold because the frame that supports the platform is attached to the vertical rails of the end ladders and thus its width is determined by the width of the end ladders. More generally, the frame that supports the platform and the frame attachment to the end ladders provide the structural stability in addition to the support for the platform of the tower scaffold disclosed in this patent.
Similarly, the scaffolds disclosed n U.S. Pat. No. 3,690,407 to Cullison and U.S. Pat. No. 3,213,964 to Tucker must be disassembled when they have to be moved through an opening that is narrower than the ladder ends.
U.S. Pat. No. 4,534,447, issued to Champigny, is for a scaffold similar to the scaffold invented by Stegath. The Champigny scaffold also has two end ladders and one horizontal truss. The Champigny truss has a pivot at each leg post and one pivot or folding configuration in the center, whereas the Stegath scaffold has two pivots in the center portion of the truss. The center pivot of Champigny folds towards the center of the scaffold as the end ladders are pushed together. This scaffold presents the same problems apparent in Stegath. The scaffold only has three sides. The horizontal stability for the fourth side is provided by the planks, which are usually attached to the uppermost ladder rung. Thus this scaffold loses the rigidity found in conventional scaffolds. Also, the Champigny scaffold is one, permanently connected unit, which makes storage difficult and inefficient.
U.S. Pat. No. 3,498,412 issued to Best, discloses a foldable scaffold with similar problems. This scaffold has four sides, but the horizontal sides are connected to the end ladders by swivel sleeves, which are free to rotate at all times including when the scaffold is in use. The scaffold is braced only by the placement of the top platform, which leaves the bottom portion of the scaffold less rigid and less secure. The Best scaffold is also intended to be permanently connected by bolts and disassembly of the Best scaffold would require much valuable time. Because the Best scaffold is permanently connected, the scaffold has an awkward and space consuming shape when in a folded position. Storage of the Best scaffold, like storage of the scaffolds previously discussed, is again difficult and inefficient.
U.S. Pat. No. 2,599,670 issued to Thomas, discloses a scaffold with four sides. Each side is connected to a post in a manner that permits the post to rotate freely. The post is able to rotate freely when the scaffold is in use. Rotation of the post is prevented by a top mounted support plank. The support plank is the only means of stabilization. The support planks are merely held in by clips and are placed at the top of the scaffold. The Thomas scaffold is also one permanently connected piece which makes storage difficult and inefficient.
Essentially, the prior art of foldable scaffolds has attempted to satisfy the demands of quick and easy assembly, simple disassembly, and compact storage while maintaining rigidity. The scaffolds are difficult to store because the shape of the folded scaffolds do not enable efficient stacking and are awkward to handle. The prior art scaffolds are easy to assemble in one unit, but rigidity and stability have been sacrificed. Rigidity and stability are sacrificed by having only three sides or by the location of the stabilizing members at the top of the scaffold.
Stacking scaffold units which are permanently attached makes assembly and disassembly very difficult. Each unit is heavier to lift, and the various pivots make lifting and orienting the scaffold awkward and time consuming. Further, as the units are stacked to provide greater elevation, the lack of rigidity in the bottom portions of the scaffold units is magnified by the increased weight and height of the scaffold structure. Also, because the prior art scaffolds rely on the support planks to provide stability, those planks will have to be left in place as the scaffold is made larger. Thus, many planks will have to be brought to the workplace, and the primary function of the plank, which is providing a worker a place to work, will be lost. A worker may also be wary of ascending a tall scaffold with only three sides or a scaffold that is free to rotate.